In a cylinder head of a reciprocating engine, a combustion surface for defining a combustion chamber has a high temperature, and thermal stress is generated. Therefore, the stress concentrates on a portion of the cylinder head which has low rigidity, and cracking or breakage may occur.
In Patent Literature 1, there is disclosed a technique in which thermal stress and thermal distortion generated on a lower surface of the cylinder head are effectively alleviated and absorbed by forming an arc-shaped groove to follow a curvature of the combustion surface of a bottom wall portion of the cylinder head defining the combustion chamber.
In the above-described reciprocating engine, a water chamber through which cooling water flows may be formed around intake/exhaust ports of the cylinder head or the like to alleviate the thermal stress and the thermal distortion of the cylinder head.